Polymer blending techniques have been reported for improving the impact resistance of materials for automotive bumpers or for interior or exterior automotive parts. For example, a propylene polymer such as a propylene homopolymer, propylene/ethylene block copolymer or propylene random copolymer is blended with an ethylene/propylene copolymer (see JP-A-57-55952; the term "JP-A" as used herein means an "unexamined published Japanese patent application"), an ethylene/.alpha.-olefin copolymer (see JP-A-4-372637, JP-A-5-331348, JP-A-6-192500, and JP-A-6-192506), a hydrogenated styrene/diene block copolymer (see JP-A-7-53842), or the like.
A generally employed method for imparting paintability to those compositions is to add an EPR (ethylen-propylene rubber) having an extremely low molecular weight. Besides this, other techniques have been proposed which include a technique comprising adding a polyolefin modified with a compound having a polar group (see JP-A-6-157838), in particular, adding a polyolefin modified with an unsaturated compound having a hydroxy group (see JP-A-5-39383), and a technique comprising adding an oligomer having a terminal polar group (see JP-A-3-157168, JP-A-5-117458, and JP-A-5-320442).
However, materials produced using the above-described techniques are disadvantageous in that an EPR having an extremely low molecular weight or a chemically modified compound as described above should be added in a large amount in order to form a coating film having sufficient solvent resistance, and the incorporation thereof tends to significantly reduce impact resistance and other mechanical properties.
Furthermore, even if a material having a good balance between paintability and impact resistance is obtained with any of those conventional techniques, such a material has a drawback that its impact resistance, especially DuPont impact strength, is reduced by painting.
In the case of exterior automotive parts, in particular, a high degree of paintability is required so that the coated parts can withstand contacts with organic solvents, e.g., gasoline.